Take your pick:
http://www.dreamviews.com/
http://www.lucidity.com/LucidDreamingFAQ2.html
http://www.xs4all.nl/~pasquale/TTM/1/index.html
It happens to me a lot, but my dreams are usually pretty much like reality, with slight weird differences. So I'm thinking, "Am I dreaming?" and do stupid things to make sure I am. By the time I figure it out, my alarm goes off.
